<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        body {
            width: 250px;
            height: 350px;
            margin: 0 auto;
        }
        
        p {
            margin-left: 25px;
            width: 200px;
            height: 300px;
            overflow: scroll;
            background-color: aquamarine;
        }
        
        input {
            float: left;
        }
        
        button {
            float: right;
        }
    </style>
    <script>
        window.onload = function() {
            var info = document.getElementById('info');
            // 检测滚动条时间
            info.onscroll = function() {
                console.log(parseInt(info.scrollHeight - info.scrollTop), info.clientHeight);

                if (parseInt(info.scrollHeight - info.scrollTop) === info.clientHeight) {
                    console.log('ok')
                        // document.getElementById('checkbox').removeAttribute('disabled');
                        // document.getElementById('button').removeAttribute('disabled');
                    document.getElementById('checkbox').disabled = false;
                    document.getElementById('button').disabled = false;
                }
            };
        };
    </script>
</head>

<body>
    <p id="info">请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款 请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款 请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款 请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款请仔细阅读条款
    </p>
    <input type="checkbox" name="checkbox" id="checkbox" disabled>已阅读
    <button type="button" disabled id='button'>注册</button>
</body>

</html>